System and method for controling contact between members in operable communication
Disclosed herein is a system to control a contact force and a positional relationship between members in operable communication. The system comprising, a first member, a second member in operable communication with the first member, and a contact force and a positional relationship exists between the first member and the second member. The system further comprising first biasing members being configured to bias and position the first member, and the contact force and positional relationship are influenced by a response of the first biasing members to the contact forces between the members in operable communication.
Backlash is a major source of undesirable noise in gear assemblies. Backlash allows the teeth of one gear to, momentarily, lose contact with the teeth of the mating gear. The noise is generated, by a tooth-to-tooth impact that occurs, when the teeth of the two gears reestablish contact with one another. The momentary loss of contact between meshing teeth often happens during specific operating conditions of the gear assembly. Such conditions include; during excessive vibration and during directional changes of at least one of the gears, for example.
Typical gear assembly design practices rely upon geometric tolerancing to position meshed gears in operable relation to one another. However, due to variation in build tolerances and component wear, clearances have to exist between the teeth of meshed gears, thereby allowing backlash, and the undesirable noise associated with it to persist.
In addition to noise, clearances may also cause degradation in operational efficiency of the meshed gears due to the contact point between the gear teeth deviating from the preferred design location. The contact force between the meshed gears is one major cause of this deviation. The contact force includes a radial component that acts in a direction to separate the gears from one another. Consequently, any clearances in the meshed gears may be biased to increase the distance between the axes of the gears resulting in reduced meshing engagement. The reduced meshing engagement alters the contact point between the meshed gears, which may result in a loss of efficiency and strength.
Typical methods employed to minimize these clearances include both springs and dampers. The springs are used to bias the gears toward one another in an attempt to assure that the gears are fully meshed together regardless of the clearances. However, the spring forces necessary to maintain the gears in full meshed engagement cause a loss in efficiency due to an increase in friction between the meshed gear teeth. Dampers are employed to allow for use of springs with lesser biasing forces. Such lighter force springs create a preload when the gears are not operationally engaged. A high damper stiffness is used to counter the separational forces of the meshed gears and to thereby reduce the backlash and loss of efficiency that results from the gears moving away from one another.
During operation, the load put on the dampers varies significantly as the operational conditions of the meshing gears change. For the dampers to successfully counter these varying forces the damper coefficients of the dampers must vary depending on the operating conditions of the gear assembly. It may be possible to create variable dampers, and algorithms to control them, based upon the operational conditions of the meshed gears. However, such systems may be highly complex, costly, and still have negative effects on the operational efficiency of the assembly.
Accordingly, there is a need in the art for a concept that automatically eliminates backlash and maintains a desired positional relationship of the meshing gears regardless of the operating conditions of the meshed gears.
BRIEF DESCRIPTION OF THE INVENTIONDisclosed herein is a system to control a contact force and a positional relationship between members in operable communication. The system comprising, a first member, a second member in operable communication with the first member, and a contact force and a positional relationship exists between the first member and the second member. The system further comprising first biasing members being configured to bias and position the first member, and the contact force and positional relationship are influenced by a response of the first biasing members to the contact forces between the members in operable communication.
Further disclosed is a method of controlling the contact force and positional relationship of operably communicating members. The method comprising, operably coupling a first member to a second member with biasing members such that an operational contact force and a positional relationship exists between the first member and the second member, and adjusting the operational position and contact force through response of the coupling of the first member to the second member.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
Referring to
Of particular interest, in this embodiment, is the relationship of the first member 14, in the first position 36, as compared to the first member 14′ in the second position 36′. Specifically, the geometric requirement that as the first member 14 is moved from the first position 36 to the second position 36′ it undergoes movement in both an X and a Y displacement, if the biasing members 22 were rigid, according to a Cartesian coordinate system 40, as depicted by Δx and Δy. This geometric relationship will be utilized to control operational contact forces and a positional relationship of the first member 14 with respect to a second member 44 as will be described in more detail below. Movement in the third dimension orthogonal to the X and Y axis may be adequately controlled and limited by conventional means of retaining the bearings 48, shown herein as ball bearings 49 in bearing housing 50 (
As mentioned above, the movement in the Y direction of Δy would occur if the members 22 were rigid, however they are not. Biasing members 22 are flexible along their length and provide an urging force against increases in length of members 22. Therefore, it is possible for the first member 14 to move from the first position 36 to the second position 36′ while not moving in a Y direction at all. Without a movement in the Y direction the members 22 must increase in length as the first member 14 moves in an X direction. Such an increase in length is accompanied by an increase in force in the minus Y direction.
In addition to the urging forces in the Y direction generated by the biasing members 22 in response to movement of the first member 14 in an axial direction, there is an axial urging force generated by second biasing members 28. Second biasing members 28 pivotally connect opposing axial ends 24 and 25 of the first member 14 to the housing 18. The second biasing members 28 work together to increase the axial forces on the first member 14 in response to the first member 14 moving in an axial, or X, direction. The force versus displacement for all biasing members 22, 28 will be discussed with reference to
Referring now to schematic 110 of
The operational communication results in forces, from the second member 44, acting on the first member 14 in both X and Y directions per the Cartesian coordinate system 40. A pair of second biasing members 28, shown here as springs, which bias the first member 14 relative to the housing 18, resists movement of the first member 14 in the X direction. First biasing members 52 anchor the first member 14 to the housing 18, and support third biasing members 56, shown here as springs, in resisting movement of the first member 14 in a plus Y direction, similar to the way biasing members 22 resisted movement of the first member 14 in reference to
where, L is the length of the biasing members 22. Accordingly, the forces acting on the first member 14 from the operational communication result in the first member 14 moving in a plus X direction and a corresponding minus Y direction, from a first operational position 36 to a second operational position 36′. The intended minus Y movement of the first member 14 moves the first member 14 towards the second member 44, thereby increasing the meshing engagement of the teeth 64, 66 if the third biasing members 56 were rigid. The third biasing members 56, however, are not rigid but are in fact flexible. The flexibility of the third biasing members 56 is controlled by the nonlinear spring constant referred to in
The novel mounting of the first member 14, of the embodiments disclosed herein, permit the force in the minus Y direction, generated by the third biasing members 56, to increase without requiring the first member 14 to move in a Y direction at all. This force increase results from a movement of the first member 14 in an X direction, which results in an elongation of the third biasing members 56 and a corresponding increase of force in the minus Y direction applied to the first member 14. Thus a force loop is created between the axial, X directional force, and the radial, Y directional force, of the contact force. The parameters of this force loop can be tailored for particular applications by adjusting the lengths of the biasing members 56, the force versus deflection curves of the biasing members 56 and the angles of contacting surfaces of the operably communicating members 14, 44, for example. Referring to
Referring to
Referring to
The single flank contact of diagram 60 has less frictional forces and therefore has higher efficiency than the double flank contact of diagram 70. However, single flank contact has the potential for noise during directional changes of the members 14, 44, or during vibration of the full assembly. In the case of a directional change of the first member 14, for example, there is potential for the tooth 64 to momentarily loose contact with the teeth 66. That is, the single flank contact between flank 72, of the tooth 64, and flank 82, of the teeth 66, may be broken before single flank contact is established between flank 74, of the tooth 64, and flank 84, of the teeth 66. This momentary loss of contact may cause an undesirable, “impact,” noise to occur when contact is reestablished.
Referring again to
Although it appears that at the precise moment when the double flank contact is attained, there may be an undesirable impact noise, the magnitude of such an impact may be controlled to a sufficiently low level to prevent it from being objectionable. This control is possible due to the force relationship between biasing members 28 and 56 and the length of member 52. Before the first member 14 can change direction it must first come to a momentary stop. At this instant as long as the natural frequency of member 14 combined with member 28 in the X direction is higher than the possible frequency that member 44 can achieve, the single flank contact condition will not change. Similarly, during vibration, the single flank contact is maintained as long as the biasing force, of the third biasing members 56, is enough to pull the first member 14 to the preferred position in the Y direction.
Although the preload in the foregoing embodiment is generated by the third biasing members 56, it could also be provided by the first biasing members 22 which has a biasing means incorporated therein. Similarly, alternate embodiments of first biasing members such as biasing members 122 of
In addition to providing preload forces, the biasing members may prevent excessive movement of the first member 14. Travel limiters 58 may be used in parallel with the third biasing members 56 of schematic 110. The bottoming out of the travel limiters 58 against hard stops 59 prevent further travel of the first member 14 away from the second member 44. A travel limiter 58 may be desirable to limit travel of the first member 14 that may be detrimental to performance of the assembly, for example. Travel limiters 58 that contact hard stops 59, however, may themselves result in audible noises depending on the speed of the travel limiters 58 when they make contact with the hard stops 59. Alternate embodiments that limit travel without hard stops 59 may be desirable and will be discussed in more detail below.
Referring to
Another embodiment of the invention, shown as schematic 140 in
Another embodiment of the invention, shown in schematic 150 of
It should be noted that all of the biasing members 22, 28, 52, 56, 122, 132, 136, 152, and 156 from the various embodiments shown may incorporate the soft hard stop effect as described above in reference to
Additionally, by configuring the biasing members 22, 28, 52, 56, 122, 132, 136, 152, and 156 to the housing 18 per embodiments of the invention as described in
Additional noise reduction may be accomplished by limiting the transmission of vibration and noise from the first member 14 to housing 18. Additional attenuation may be achieved by forming the biasing members 22, 28, 52, 56, 122, 132, 136, 152, and 156 from layered material where the layers consist alternately of metal and polymer materials, for example. Such a construction, often referred to constrained-layer-damping, is commonly used for purposes of noise reduction.
Embodiments of the invention may include some of the following advantages: automatic reduction or elimination of backlash, reduced noise levels associated with backlash, reduced vibrational noise levels, automatic control of positional relationship of members in operable communication, automatic control of contact force between members in operable communication, automatic adjustment of mesh engagement at all load levels, improved control of meshing engagement, improved meshing efficiency, symmetry for opposite directional motion and elimination of hard stops in biasing members.
While the embodiments of the disclosed method and system have been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the embodiments of the disclosed method and system. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the embodiments of the disclosed method and system without departing from the essential scope thereof. Therefore, it is intended that the embodiments of the disclosed method and system not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the embodiments of the disclosed method and system, but that the embodiments of the disclosed method and system will include all embodiments falling within the scope of the appended claims.
Claims
1. A system to control a contact force and a positional relationship between members in operable communication, the system comprising:
- a first member;
- a second member in operable communication with the first member, and a contact force and a positional relationship exists between the first member and the second member; and
- first biasing members being configured to bias and position the first member, wherein the contact force and positional relationship are influenced by a response of the first biasing members to the contact forces between the members in operable communication.
2. The system as in claim 1, wherein the response includes a change of biasing force in response to movement of the first member from a first operational position to a second operational position.
3. The system as in claim 2, wherein the change in biasing force of the first biasing members or second biasing members or third biasing members are nonlinear with the change from the first operational position to the second operational position.
4. The system as in claim 2, wherein the movement of the first member from the first operational position to the second operational position is substantially axial relative to the axis of the first member.
5. The system as in claim 3, wherein the second biasing members resist movement of the first member in an axial direction.
6. The system as in claim 1, wherein the first member is a worm and the second member is a worm gear.
7. The system as in claim 6, wherein the operational contact force is due to contact between the gears.
8. The system as in claim 1, wherein the operational contact force includes a preload configured to urge the first member towards the second member.
9. The system as in claim 8, wherein the first biasing members or third biasing members are configured to provide an urging force thereby creating the preload.
10. The system as in claim 1, further comprising third biasing members being configured to couple to the first biasing members, the third biasing members being further configured to provide an urging force to influence the response of the first biasing members.
11. The system as in claim 10, wherein the first biasing members or the third biasing members are configured as flexible shaped members.
12. The system as in claim 11, wherein the flexible shaped members are configured as bowed members.
13. The system as in claim 10, wherein the first biasing members or the third biasing members comprises a plurality of layers.
14. A method of controlling the contact force and positional relationship of operably communicating members, the method comprising:
- operably coupling a first member to a second member with biasing members such that an operational contact force and a positional relationship exists between the first member and the second member; and
- adjusting the operational position and contact force through response of the coupling of the first member to the second member.
15. The method of claim 14, further comprising:
- moving the first member from a first operational position to a second operational position in response to a change in operational contact force between the first member and the second member.
16. The method of claim 14, further comprising:
- increasing the contact force in response to moving the first member from the first operational position to the second operational position.
17. The method of claim 14, further comprising:
- preloading the operational contact force between the first member and the second member.
18. The method of claim 14, further comprising:
- damping noise transmission through the biasing members with a plurality of layers.
19. The method of claim 14, further comprising:
- controlling mesh engagement through changes in operational contact force wherein the first member is a worm in mesh with the second member which is a worm gear.
20. The method of claim 14, further comprising:
- biasing the first member axially with axial biasing members.
Type: Application
Filed: Jul 20, 2006
Publication Date: Feb 21, 2008
Patent Grant number: 8250940
Inventors: Suat Ozsoylu (Rochester Hills, MI), Michael J. Augustine (Mayville, MI)
Application Number: 11/489,761